1. Field of the Invention
The present invention relates to a vibration damping device for a drive system of a motor vehicle comprising a base body rotatable about an axis of rotation and a deflection mass arrangement arranged in the base body and having at least one deflection mass and a deflection path which is associated with the at least one deflection mass and along which the deflection mass can move during rotation of the base body about the axis of rotation, wherein the deflection path has a vertex area and deflection areas on both circumferential sides of the vertex area and the deflection areas have a decreasing distance from the axis of rotation proceeding from the vertex area toward their circumferential end areas.
2. Description of the Related Art
A vibration damping device is known from DE 44 26 317 A1 having a plurality of deflection paths arranged at a base body and distributed about the axis of rotation of the base body. A plurality of deflection masses are respectively movably arranged for moving along these deflection paths. The deflection paths for the deflection masses are curved toward the axis of rotation. When torsional vibrations occur, the deflection masses are deflected from the vertex areas of the deflection paths and approach the axis of rotation. As they approach the axis of rotation, the deflection masses change centrifugal potential and thereby absorb energy. In this way, there is generated an oscillation of the individual deflection masses which opposes the exciting vibrations and which leads to the damping or elimination of defined excitation frequencies. Vibration damping devices of this kind are especially suitable for damping higher harmonic oscillations of vibrations which are generated by ignitions occurring periodically in an internal combustion engine.
The individual deflection masses roll during their movement along the deflection paths so that energy is not only transferred in the displacement of the deflection masses in centrifugal potential, but is also converted into the rotational energy of the individual deflection masses. Accordingly, to adapt the deflection mass and deflection path configuration to a determined excitation frequency to be damped, there must be a defined relationship between the deflection of the individual deflection masses, i.e., the displacement in centrifugal potential, and the energy changed into the rolling movement. However, when the deflection masses approach the end of the deflection path, the contact pressing forces which are generated by the centrifugal force and by which the individual deflection masses are pressed against the deflection paths decrease because of the increasing curvature of the paths. The decrease in the contact pressing forces changes the friction ratios in the area of contact of the deflection masses at the associated deflection paths, thereby increasing the risk, especially in the end area of the individual paths, that a transition from a rolling movement to a sliding movement will occur and place the natural frequency of the oscillators out of tune. The detuning of the natural frequency results in the loss of the adjustment to the frequency to be damped and the vibration damping device no longer fulfills its function in a satisfactory manner.
An object of the present invention is to provide a vibration damping device which prevents the risk of an undefined detuning of the natural frequency.
According to an embodiment of the present invention, this object is met by a vibration damping device, in particular for a drive system of a motor vehicle, comprising a base body which is rotatable about an axis of rotation and a deflection mass arrangement arranged in a base body and having at least one deflection mass and a deflection path which is associated with the at least one deflection mass and along which the deflection mass can move during rotation of the base body about the axis of rotation. The deflection path has a vertex area and deflection areas on both sides of the vertex area. The deflection areas have a decreasing distance from the axis of rotation of the base body proceeding from the vertex area toward circumferential end areas of the deflection areas.
The vibration damping device according to the invention further comprises a positive rolling arrangement via which the at least one deflection mass rolls during the movement of the at least one deflection mass along the associated deflection path.
Accordingly, appropriate steps are taken in the vibration damping device according to the invention to compel the rolling movement of the at least one deflection mass and thereby prevent the transition to a state of sliding motion. Throughout the length of the deflection path and especially in the area of the respective ends of the deflection paths and when sharp changes in rotational speed occur, the at least one deflection mass moves along the associated deflection path while carrying out a rolling movement so that a defined proportion of the excitation energy is changed into rotational energy in these movement states or path areas. The detuning of the natural frequency occurring in the prior art due to undefined movement behavior is therefore prevented.
The positive rolling arrangement may, for example, comprise a toothing arrangement acting between the at least one deflection mass and the base body or a component connected therewith.
Since the at least one deflection mass generally moves on the associated deflection path, it is suggested that the toothing arrangement comprises a toothing provided at an outer circumference of the at least one deflection mass and a counter-toothing provided at the deflection path.
In the above embodiment, the toothing may extend over a portion of the width of the outer circumferential surface of the at least one deflection mass. In this way, a functional separation is provided such that a smooth rolling surface is still provided while the rolling movement is nevertheless compelled in another surface region at the same time.
To prevent the occurrence of an unwanted tilting movement of the at least one deflection mass due to this functional separation, it is suggested that the width portion of the toothing comprises at most one half of the total width of the outer circumferential surface.
To achieve a round rolling movement in which the influence of the toothing is minimized, it is suggested that the toothing and the counter-toothing are constructed essentially only for the transmission of forces directed approximately along the deflection path. That, is, the individual teeth of the toothing act only to compel the rolling movement when, upon the occurrence of minimum sliding movement, a slight movement play between the teeth of the toothing and counter-toothing is overcome and the teeth accordingly strike against one another by their respective flanks in the direction of the deflection path. In particular, however, essentially no substantially orthogonal forces relative to the respective deflection path are transmitted between the toothing and the counter-toothing. This means that the toothing and counter-toothing do not absorb any centrifugal force components pressing the respective deflection masses radially outward.
Furthermore, the at least one deflection mass may have at least one guide pin which is movable along a guide path during the movement of the at least one deflection mass along the deflection path. To achieve the above-mentioned functional separation between compelling the rolling movement and receiving the centrifugal forces also in a construction of this kind, it is suggested that the toothing arrangement acts between the at least one guide pin and the associated guide path. In a construction of this kind, the at least one deflection mass may continue to be supported at the associated deflection path under the influence of the centrifugal forces, but the compelling of the rolling movement is effected in the area of the at least one guide pin and the associated guide path, i.e., remote from the centrifugal support.
Alternatively, an opposite arrangement may also be used in that the deflection mass is supported during movement at the guide path associated with the at least one guide pin and in that forces directed substantially only approximately along the deflection path may be transmitted between the toothing and the counter-toothing.
In this embodiment, the at least one deflection mass is supported at the guide path and the deflection path essentially receives no forces that are directed radially outward. In contrast, a rolling movement of the at least one deflection mass is compelled by the toothing arrangement provided in the area of the deflection path and outer circumference of the at least one deflection mass, wherein this toothing arrangement is now substantially kept free from centrifugal forces.
In an alternative embodiment, the positive rolling arrangement may comprise a guide projection/guide path arrangement by which a rolling movement of the at least one deflection mass is generated during deflection of the at least one deflection mass out of the vertex area of the associated deflection path. In this way, a transmission mechanism is introduced, wherein when the respective deflection mass attempts to move along the deflection path, this transmission mechanism compulsorily moves these deflection masses in a rolling movement.
For example, the guide projection/guide path arrangement may comprise at least one guide projection which is offset with respect to a rolling axis of the at least one deflection mass, i.e., is not centric relative to the at least one deflection mass, and a guide path associated with this guide projection. Further, a guide projection may be arranged at the at least one deflection mass so as to be concentric to a rolling axis thereof, and that the guide path associated with this guide projection is provided at the base body or at a component connected with the latter and essentially follows the course of the deflection path.
To achieve a movement of the at least one deflection mass with as little squeezing or jamming as possible, the guide projection/guide path arrangement comprises at least two guide projections and guide paths associated therewith and that the at least two guide projections are provided at the same axial sides or at different axial sides with respect to the rolling axis of the at least one deflection mass.
A further improved guiding action in the introduction of the positive rolling movement may be achieved when the guide projection/guide path arrangement comprises two groups of guide projections and guide paths associated with the latter and when one of the groups of guide projections with associated guide paths is provided at every axial end side of the at least one deflection mass with respect to the rolling axis of the same.
In another alternative embodiment form, the positive rolling arrangement comprises a rolling strip arrangement surrounding the at least one deflection mass and having end areas fixed in one of the end areas of the deflection path associated with the at least one deflection mass.
In this embodiment, the rolling strip arrangement may comprise a rolling strip which loops around the at least one deflection mass by at least one turn.
To prevent a tilting of the rolling strip arrangement that is compulsorily generated during the looping, the rolling strip arrangement may comprise at least two rolling strip portions which are fixed by one end to an end area of the deflection path and by the other end to the deflection mass and which surround the deflection mass in opposite directions. In this respect, the forces on the deflection mass originating from the bending forces at the wound-on strip are canceled and enable a deflection that is extensively free from forces.
In this connection, the at least two rolling strip portions are offset with respect to one another in the direction of a rolling axis of the at least one deflection mass.
To prevent unwanted tilting of the at least one deflection mass in a construction of the type mentioned above, the rolling strip arrangement may comprise at least three rolling strip portions, wherein rolling strip portions which directly follow one another surround the deflection mass in opposite circumferential directions.
Furthermore, the at least two rolling strip portions may be connected with one another by a connection strip portion to facilitate assembly.
To dimension the deflection angle area of a respective deflection mass as large as possible proceeding from the vertex area of the associated deflection path, the rolling strip arrangement may be looped multiple times around the associated deflection mass, so that a correspondingly extensive rolling movement may be generated. However, this arrangement means that the rolling strip arrangement and the rolling strip portions will overlap in some areas when they are wound completely around the associated deflection mass and, in this overlapping area, would generate a step opposing a circular rolling movement. To prevent this step in the overlapping area, a rolling surface region is provided at the at least one deflection mass, wherein this rolling surface region is associated with every rolling strip portion and, proceeding from the area in which the respective rolling strip portion is secured to the deflection mass, is at a distance helically from the rolling axis of the deflection mass, wherein a lead or pitch of the helically extending rolling surface region substantially corresponds to the material thickness of the respective rolling strip portion.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.